The present application relates to nonaqueous electrolytes and batteries, specifically to nonaqueous electrolytes that contain an organic solvent and an electrolyte salt, and nonaqueous electrolyte batteries using such nonaqueous electrolytes.
There is a strong demand for smaller, lighter, and longer-life portable electronic devices such as camera-integrated VTRs (Video Tape Recorders), cellular phones, and laptop personal computers, which have become pervasive over the last years. In this connection, batteries, particularly secondary batteries, which are light and capable of providing high energy density, have been developed as the portable power source of such electronic devices.
Particularly, secondary batteries (lithium ion secondary batteries) that take advantage of the storage and release of lithium (Li) for the charge and discharge reaction have been put into a wide range of practical applications for their ability to provide higher energy density than other nonaqueous electrolyte secondary batteries such as lead batteries and nickel cadmium batteries.
The lithium ion secondary batteries include a positive electrode, a negative electrode, and an electrolyte. Increasing the potential of the positive and negative electrodes lowers battery characteristics, because the high-potential positive electrode active material or negative electrode active material reacts with the nonaqueous electrolyte and decomposes the electrolyte, and because the cobalt contained in the positive electrode active material dissolves out.
Concerning the composition of the electrolyte used for secondary batteries, a technique is proposed that uses a compound (nitrile compound) having a nitrile group (or a cyano group: —CN) to improve cycle characteristics and other battery characteristics. As such nitrile compounds, those having a cyanoethyl group (JP-A-2000-243442), and those having a plurality of nitrile groups (JP-T-2007-519186; the term “JP-T” as used herein means a published Japanese translation of a PCT patent application) are used. With this technique, the nitrile compound can stabilize the transition metals and transition metal oxides, and can thus suppress the dissolving of the transition metals from the positive electrode active material.